1. Field of the Invention
The present invention relates to a brazed jointed member, such as a ceramic-metal jointed member, and more particularly to a ceramic-metal jointed for use in a tappet for an engine, an engine part such as a valve lifter, a tool such as a cutting tool and an electronic part.
2. Description of the Related Art
Conventionally, an active brazing method using an active brazing material has been employed as one of methods of joining a ceramic member and a metal member. A jointed member manufacturing by using the foregoing method has been used as a rotor for a ceramic turbo charger, a ceramic tappet and the like. The active brazing method is a method for joining the ceramic member and the metal member by the active brazing material including the active metal (Ti, Zr, etc.). The active brazing method is a method which has an object to improve the strength between the brazing material and the ceramic member. In the method, a reaction layer (a diffusion layer) is formed between the brazing material and the ceramic member so that the brazing material and the ceramic member are strongly joined together. As a result, the ceramic member and the metal member can be strongly joined together.
Among the active brazing materials, a brazing material made of an In-Cu-Ag-Ti alloy and having a low melting point (the solid phase temperature: 600.degree. C. to 750.degree. C.) has been used to join up members, such as sliding parts for an automobile. A method using the brazing material is capable of reducing, to a minimum, the difference in the shrinkage (the thermal strain) occurring attributable to the difference between the thermal expansion of a ceramic member and that of a metal member. For example, a technique of directly brazing Si.sub.3 N.sub.4 and Ni-Cr-Mo steel (JIS SNCM630) by using an In-Cu-Ag-Ti alloy brazing material has been disclosed as a technique for manufacturing, for example, tappets, rocker arms or valve bridges (refer to Unexamined Japanese Patent Publication (kokai) No. 2-199073). In addition to the foregoing brazing material having the low melting point, a technique for manufacturing the foregoing sliding parts by using a brazing material (the solid temperature: 900.degree. C. or higher) among the active brazing materials has been put into practical use.
Although the above-mentioned brazing materials have been administered as the brazing materials, the jointed member has not satisfactorily been manufactured.
In addition, the jointed member joined by using the conventional brazing material has sufficient initial strength against tensile stress, compression stress and torsion stress. In addition to the above-mentioned simple stresses, practical products using the jointed member are exposed to severe conditions, such as thermal stress which is generated by to the difference between the thermal expansions of members occurring after the temperature has been changed, and fatigue due to use for a long time. Therefore, the jointed member using the conventional brazing material is sometimes unsatisfactory.
In a case of a tappet for an internal combustion engine consisting of a cam having a sliding surface formed by a ceramic member, the temperature of a joint portion including the ceramic member, the metal member (the body of the engine tappet) and the brazing material is raised to about 200.degree. C. because of heat generated during the sliding operation and engine oil. The rise in the temperature causes thermal stress to be generated due to the difference in the thermal expansion between the ceramic member (for example, Si.sub.3 N.sub.4) and the metal member. As a result, the proof stress of the brazing material deteriorates. Moreover, fatigue (fatigue of the brazing material) takes place after use for a long time. Since the brazing material is arranged to realize satisfactory reactivity with the ceramic portion, fatigue and separation between the ceramic and the brazing material does not easily take place. However, the foregoing rise in the temperature sometimes results in deterioration, such as separation, between the metal member and the brazing material when the product is used.
Since the adhesive strength between the metal member and the brazing material depends upon the degree of the wettability of the joint surface on the metal member, one might employ a method of improving the wettability to prevent separation of the metal member and the brazing material from each other. However, the foregoing method by itself does not satisfactorily increase and adhesive strength.